Numerous apparatuses and methods for the continuous gravimetric metering of flowing materials for burner systems are known from the state of the art. Flowing materials are understood as being all materials which can be used for fuelling burner systems. Coal dust and waste of all kinds, and in particular plastic waste, are hereby mentioned as examples. The flowing materials can be present both in the form of particles as well as in coarse form. The plastic waste can be shredded, e.g. shreds of waste tires or carpets, or it can be used in an unchanged way, e.g. in the form of plastic containers and packaging. The flowing materials are usually stored in a silo or bunker and supplied with the help of metering and transport apparatuses to the burner system, e.g. a rotary kiln in the production of cement.
Such systems for continuous gravimetric conveyance and/or mixing of pourable material are known for example from DE 40 23 948 A1, with a rotary metering weigher according to DE 32 17 406 A1 or EP-A-0 198 956 being used, because such a metering apparatus can be used in an enclosed pneumatic conveying path to continuously determine the flow of pourable material situated therein and the throughput of pourable material can be influenced by varying the supplied quantity of air per unit of time or by changing the speed. A computer-controlled central metering control system is used for the respective control of the desired mixture ratio or the desired conveyed quantity per unit of time (conveying rate), as is described for example in DE 32 17 406. The weighing signal of the bunker weighing cells is used as an input signal and especially the speed of the metering rotor is controlled for the supply of the pourable material.
Such an apparatus is further known from DE 44 43 053. The apparatus described therein for the continuous gravimetric metering and determination of mass flow of flowing materials comprises a flow meter, especially a Coriolis metering wheel for determining the instantaneous mass flow, and a metering device connected downstream of the flow meter. The flow meter is connected with the metering device via a metering control unit and the delivery of the metering device can be controlled in a time-shifted manner on the flow meter depending on the deviations in the mass flow.
It is becoming increasingly more important to govern the supply in such a way that the combustion process can occur in an optimal manner where the supply of flowing materials to burner systems is concerned, especially in cases where different types of flowing materials are to be supplied, as a result of environmental and economical considerations. This means that the supply of flowing materials as a fuel and the supply of air must be controlled in such a way that the combustion processes can run optimally and the desired temperature can be kept constant at the same time. The problem arises in connection with different fuels that the calorific value of the individual goods or the flowing materials cannot be determined in their entirety until the present day. For this reason, only a part of the usually employed fuels, e.g. coal dust for rotary kilns for the production of cement, are currently partly replaced by alternative fuels such as plastic waste. It is also often tried to add merely one single type of plastic material, because the calorific values of the individual types of plastic are differently high. Plastic material of a “pure assortment” has a calorific value which lies in the magnitude of crude oil, whereas fractions of mixed plastic materials as are obtained especially in waste management have a calorific value which is close to that of wood or coal.